Transcript A TOUR OF THE CELL

A TOUR OF THE CELL
BEGIN
Hello there young students. I am Mr.
Cell and I am here to help you with
your understanding of cell structures.
Sure, you could have a professor talk
about cells, but why not get it firsthand from me!
First, I would like to tell you why you
should learn about me. All living things
are made up of cells. If it isn’t a cell, it is
not classified as living. So you can well
imagine that I form the foundation for
BIOLOGY –the study of living things.
Secondly, I am ultimately responsible for the
function of all systems in multicellular organisms. If
I, and all my brother cells have a defect, the organ
will not function properly and this will lead to
problems that you observe as disorders or diseases.
Entire organs and organ systems rely upon me and
my brother cells co-ordinating our activities and
acting together to perform vital functions. If one
group of cells doesn’t perform their job, the entire
organ could malfunction or even completely fail!
IMAGINE GROUP WORK WHERE IF ONE GROUP MEMBER DOES NOT DO HIS
OR HER JOB, YOU WERE ALL TO FAIL!!! DOESN’T SEEM FAIR? WELL THAT’S
REALITY!
If you think that’s serious, consider the fact that if one
critical organ fails it can lead to the death of the entire
organism. That’s trillions of cells that die. How would you
like that responsibility?
Now I represent a particular type of cell. I am a
eukaryotic animal cell and I represent this cell type.
Watch out for my evil uncle Mr. Badbacter . He wants to take over
the world! He is a prokaryote cell
Also keep an eye out for his assistant, Mr. Badplant . He’s a little
dense. He is a eukaryotic plant cell.
What are we
going to do
today boss?
The same thing
we do every
day. Try to take
over the world!
Health professionals study me all the time to
determine pathologies such as cancer. Sometimes
just understanding the way that I normally look
and the way I look when I am diseased, can help
health professionals make a diagnosis and thus
begin the process of treatment.
Now, I hate to blow my own horn, but inside me, the
very essence of life exists. I conduct all the “burning” of
energy molecules that keeps you alive. So, you should
also understand that knowing how my internal structure
works is essential to understanding life itself.
But enough about me. Let’s first learn
I like the cancer and
about the cell theory.
diseased ideas. Sounds
evil like me!
The light microscope observations of
Hooke, Leeuwenhoek, established study
of the cell. In the 1800’s (nineteenth
century), Schleiden and Schwann
developed the cell theory. Virchow
contributed the third postulate
1.All living things are made up of cells
2.Cells are the structural and functional
units of organs
3.All cells come from pre-existing cells
You know, those scientist guys could
finally see me but they still didn’t know
that I caused a whole bunch of diseases!
Now, before we take a look at my internal
structures, you have to understand that
developments in microscopy were necessary
in order to see the details of the tiny
structures inside me.
The initial work was accomplished with light microscopes. It still remains
the most common way of examining cells. Light microscopes typically
have a maximum magnification of about 2000X with oil immersion. This
is because of resolution limits of light itself.
Further developments led to electron microscopes which did not have the
limitations of resolution because they used electrons rather than light.
This led to a much greater magnification (up to 2 million times) but only a
photograph was possible for examination. Due to the fact that specimens
has to be thin, dry (desiccated ) and dead, the electron micrographs also
were difficult to interpret.
Development of the scanning electron microscope allowed for electron
microscope 3-D images which were much easier to interpret. Resolution
and thus magnification are less than that of the TEM.
OH CANADA!
The first practical electron
microscope was developed at
the University of Toronto!
Now lets play match the microscopes to their pictures!
Hey, what are you doing? Stop! That’s my
nucleus!
I can’t survive without the nucleus. It holds
and protects all the genetic information
needed to regulate me. If I need to fix
something or manufacture an enzyme, the
nucleus is the only organelle that will
provide the information.
I don’t need a nucleus.
All I need is just my
circular strand of DNA
Hey boss, I’ve got a
nucleus
N U C L E U S – THE DETAILS
The main purpose of the nucleus is to separate the nuclear contents from the
cytoplasm. This is accomplish by the nuclear membrane(envelope). This is
important as many normal cellular processes occurring in the cytoplasm could
damage the DNA There are actually two lipid bilayer membranes, the inner
surrounds the nucleoplasm and contains the nuclear lamina that contain filaments
necessary to maintain the nucleus shape. The outer is continuous with the rough
endoplasmic reticulum. The two membranes fuse at the nuclear pores. These are
small perforations in the nuclear membrane that allow the RNA molecules to exit
the nucleus.
NUCLEOLUS- location of ribosomal RNA
molecule manufacture
The three different RNA molecules, transfer
tRNA, messenger mRNA and ribosomal r
RNA, are all copied from the original DNA
strand.
TIP –the nucleolus is not surrounded by a
membrane. Remember that plural for
nucleolus is nucleoli!
You can see the nuclear pores in this picture.
These allow the passage of the ribosomal RNA
subunits and other RNA chemicals mRNA and
tRNA into the cytoplasm.
DNA stores the hereditary material. The
chromatin is a combination of DNA and
protein. It floats in the nuclear fluid
called the nucleoplasm.
In this electron micrograph you can see the
rough endoplasmic reticulum (the line
with the dots) and how it connects the the
inner nuclear membrane at the nuclear
pores.
The euchromatin contains information that
codes for genes that are expressed. The
heterochromatin is repetitive information
that is not expressed.
Don’t get confused with language.
Nuclei is the plural form for the nucleus. Some
cells, ex. Heart muscle cells, are
multinucleated. That means they contain two
or more nuclei. This can be confused with the
term nucleoli. This is the plural of a nucleolus.
Many cells have many nucleoli such as liver
cells. Many nucleoli are indicative of much RNA
synthesis and correspondingly a large amount
of protein product.
Also the nucleus is an organelle but the
nucleolus is not as it does not have a
membrane
RIBOSOMES – Not organelles but darn important!
These are my ribosomes. They are responsible for protein synthesis.
Remember- they were made in the nucleus!
These dots are my ribosomes attached to my endoplasmic
reticulum and called bound ribosomes. Ribosomes can also
be found freely floating in the cytosol and are appropriately
called free ribosomes.
RIBOSOME= PROTEIN FACTORY
Ribosomes attach the messages from DNA that have been imprinted on the
messenger RNA (mRNA) to the appropriate transfer RNA (tRNA) and in doing this
they sequence the correct amino acids to make specific proteins.
The ribosomes are made up to two ribosomal RNA (rRNA) subunits. In eukaryotes, there
is a small component 40s and a large component 60s. These are made separately in the
nucleus and assembled in the cytoplasm into the ribosome
Hey! I got them
things too but they
are smaller
Prokaryotic ribosomes are
made of one 50s and one 70 s
subunit.
My ribosome is bigger
than by boss’s
ENDOPLASMIC RETICULUM – FRAMEWORK FOR PROTEIN ASSEMBLY-TRANSPORT
Okay, now you are getting me angry. You are
unravelling my endoplasmic reticulum. I need those
membranes to act as channels to move chemicals in
my body. It is very similar to the plasma membrane.
I usually attach ribosomes to the endoplasmic reticulum.
This is called Rough endoplasmic reticulum. Since the
ribosomes are the site of protein synthesis, the rough ER
would manufacture my proteins. The protein enters the
ER lumen and folds into its native conformation(shape).
Most secretory proteins are glycoproteins. carb+protein
The secretory proteins exit via transport vesicles that bud
like bubbles from the transitional ER.
If no ribosomes are attached, the endoplasmic reticulum is called the
Smooth endoplasmic reticulum. Fats and steroid sex hormones are
produced by the smooth ER. The smooth ER is also responsible for
carbohydrate metabolism, calcium regulation and drug detoxification.
Electron micrograph of
the ROUGH ER. Notice
the little round dots
that are the ribosomes.
Liver and pancreas cells
are rich in RER
Electron micrograph of
the SMOOTH ER. Cells in
organs such as the
ovaries and testicles are
rich in smooth ER due to
their production of sex
hormones like estrogen
and testosterone.
You can
find ER in
me too.
MITOCHONDRIA –KREBS AND ETC ENERGY POWER PLANT
Hey, what are you grabbing at now? That’s my
mitochondrion. I need those to produce energy
efficiently. Without the mitochondrion, I will not
have the Krebs cycle and electron transport chain
to increase my ATP output.
The mitochondrion has its own DNA which is used to
replicate more mitochondria. In this case, the
mitochondria are different than other organelles
because they do not rely on the genetic information
within the nucleus.
I don’t need no
stinking
mitochondria.
I’ve got mitochondria
boss. They let me do
the Krebs cycle and ETC
to get more energy
Mitochondria –powerhouse makes ATP
Mitochondria have two membranes, an outer and an
inner membrane . The inner membrane is folded and
these folds are called cristae. Inside the inner
membrane is the matrix, where the Krebs cycle
occurs. The space between the inner and outer
membranes is called the intermembrane space.
Free ribosomes and the mitochondia’s own
DNA are found inside the matrix.
Don’t get
BIOCHEMICAL ACTIVITY
the
Each pyruvate molecule produced by glycolysis is
cristae
actively transported across the inner mitochondrial
confused
membrane, and into the matrix. Pyruvate is then
with the
combined with Coenzyme A into acetyl CoA and enters cisternae
the Krebs cycle in the matrix. The electron transport
of the
chain sends hydrogen ions (protons)into the
Golgi
intermembrane space. These protons accumulate in
the intermembrane space developing a higher
These mitochondria
concentration here as opposed to the proton
appear circular because of concentration in the matrix. Due to this gradient, the
the plane of cut in this
protons will re-enter the matrix through the ATP
electron micrograph.
synthase sites generating ATP.
The brown fat function in mammals.
Brown fat is rich in mitochondria unlike white fat which is common
An unusual process known as proton leak or
mitochondrial uncoupling can generate heat in animal
cells. It allows protons to re-enter the mitochondrial
matrix without contributing to ATP synthesis. It is due
to the proton channel called thermogenin . Protons
enter the matrix and the unharnessed potential energy
is released as heat.[Thermogenin is primarily found in
brown fat, and is responsible for an alternate method
of thermoregulation.
Hey, this
brown fat stuff
keeps me
warm during
hibernation.
I’ve got brown
fat to help keep
me warm . It’s
on my back and
spine
DID YOU KNOW?
The cell must receive mitochondria during the
process of mitosis. This is accomplished during
cytokinesis. If a cell were not to receive
mitochondria it cannot make them on its own and
will be unable to conduct the Krebs cycle and
Electron transport chain.
The inner membrane of the mitochondrion is more
similar to prokaryote plasma membranes than
eukaryote cell membranes. This supports the
theory of ENDOSYMBIOSIS --Find out more
Now you are grabbing my
cytoskeleton.
Hey, I need those to
maintain my..........
SHAPE!
The eukaryotic cytoskeleton. Actin
filaments are shown in red,
microtubules in green, and the nuclei
are in blue.
THREE COMPONENTS OF CYTOSKELETON
1.MICROTUBULES: hollow cylinders made of tubulin –
resist compression -behave like little sticks
2.MICROFILAMENTS –ACTIN FILAMENTS
resist tension and maintain cellular shape LIKE CABLES
3.INTERMEDIATE FILAMENTS
Resist tension and maintain cellular shape LIKE
CABLES but are more STABLE than ACTIN FILAMENTS
Here’s a chart to show and
compare the applications of my
filaments.
microtubule
microfilaments
Intermediate filaments
Cell shape maintain
Cell shape maintain
Cell shape maintain
Cilia
Cell shape changes
Anchor organelles
Chromosome
movement
(celldivision)
Cleavage furrow
(celldivision)
Form nuclear lamina
Organelle movements
Cytoplasmic straming
Motility (pseudopod)
Muscle contraction
The cytoskeleton is a dynamic structure that maintains
cell shape, protects the cell, enables cellular motion
(using structures such as flagella, cilia and lamellipodia),
It plays important roles in both intracellular transport
(the movement of vesicles and organelles) and cellular
division.
Hey boss, since
I’m also a
eukaryote, that
means that I got a
cytoskeleton too.
Say boss, what is a lamellipoda?
Ya you got a
cytoskeleton.
Even I have a
cytoskeleton you
dimwitted plant.
Lamellipodia are a
characteristic
feature at the front,
leading edge, of
motile cells like my
enemy, the white
blood cells
The cytoskeleton was
previously thought to
be a feature only of
eukaryotic cells , but
homologues to all the
major proteins of the
eukaryotic cytoskeleton
have recently been
found in prokaryotes
Microtubules are made of tubulin. As shown below it is
a hollow coil.
They are organized by
the centrosome.
This is a centriole made of nine
triplet sets of tubulin. It is only
found in animal cells, is used
for cell division and a pair is
located in the centrosome .
This is a eukaryotic cilia or flagella
made up of nine doublet sets of
tubulin . Respiratory system
examples of tracheal and
bronchial cells contain ciliated
cells responsible for moving
mucus . Cilia and flagella also can
be used to move cells. Ex sperm
tails or cilia of paramecium
BASAL BODY
c.s.
Hey boss. Don’t you got a
flagellum?
NOTICE
Flagella can only be
found in some plant
sperm.
Ya, I have a flagellum but it’s
different. My flagellum is
made of the protein flagellin
and it turns like a corkscrew
to pull me through liquids My
flagella also have many
configurations as shown
below.
Some bacteria have one or
multiple flagella. This
makes them motile.ie- they
can move. Note that this a
a bacterial option and not
all species have one.
DID YOU KNOW?
Stomach ulcers were
previously believed to be
caused strictly by acid action
on the stomach lining. Now
it is understood that the
bacteria Helicobacter pylori
can cause stomach ulcers. It
uses its multiple flagella to
propel itself through the
mucus lining to reach the
stomach epithelium.
Great
work
Helio
Join my
evil gang
Golgi – Receiving and shipping—just call me Fedex
Now that structure is called by Golgi apparatus. Its purpose is
to process and package the macromolecules (mostly fats and
lipids) produced by the cell. It could be compared to a post
office as it modifies, sorts and packages substances for cell
secretion (exocytosis).
Can you see the flattened stacks in this Golgi sample. These are
called cisternae
I got
Golgi
too.
There are three types of Golgi vesicles :
1.exocytotic vesicle which fuses with the cell membrane to transport
material out of the cell
2.the secretory vesicle which remains in the cell until chemical
messengers stimulate them to be released out of the cell
3.the lysosomal vesicles –These lysosomes contain the dangerous
hydrolytic enzymes
The Golgi can be identified because they are crescent shaped flattened
sacs. Often you will see the small vesicles at the edges. The two sides of
the membrane are responsible for different functions. The trans face is
the shipping (forms vesicles) and the cis face the receiving end The ER
adds contents to the Golgi lumen on the cis side (receiving)
LYSOSOMES- a deadly bag of tricks
This is my lysosome. It contains some serious digestive enzymes,. These
enzymes are so powerful that if released, they will destroy the entire cell
contents. This autolysis is often the reason they are called suicide bags.
I constantly pump protons through the single membrane into the
lysosome creating a low pH on the inside of the lysosome . That means
the lysosome interior is acidic pH 4.8 compared to the cytosol pH 7.2.
The enzymes in the lysosome are only active at a pH of 4.5, so if some of
the enzyme were to leak out, they would not be at their optimum pH
and thus would not harm the cell interior. If, however, the lysosome
were to release its entire contents, it would lower overall cell pH and
destroy all cell contents.
Lysosomes also digest worn-out organelles, food particles, engulfed viruses or
bacteriaor other forms of waste. Lysosomes fuse with the vacuoles or other
organelles, releasing their enzymes.
Lysosomes also can digest macromolecules and prevent cell accumulation of various
molecules.
Lysosmes can also can repair damage to the plasma membrane by forming a
membrane patch, sealing the wound.
Hey boss,
do I contain
lysosomes?
Hey boss, I heard that if the
lysosome digestive enzymes are
incorrect, they can lead to cell
accumulation of harmful
materials.
Biologists believe
the lysosome is only
found in animal
cells, not plant cells.
Ya, the genetic disease Tay
Sachs is caused by that
problem leading to
impairment of metabolism.
Kind of like an evil
lysosome, huh?
PEROXISOMES – PRODUCING HYDROGEN PEROXIDE
Peroxisomes are small single
membrane enclosed sacs that act
as specialized metabolic
compartments
That’s right and they transfer
hydrogen from various
substrates to oxygen
For example liver cells use
peroxisomes to detoxify alcohol
When the hydrogen peroxide is formed in
the peroxisome, special enzymes degrade
the hydrogen peroxide (which is toxic to
cells) into harmless water. This organelle
is interesting in that is contains both the
enzymes to make and to destroy the
peroxide in the same space.
We will use these peroxisomes in our LIVER LAB!
Glyoxyxomes in the fat storing
tissues of plant seeds are a
type of peroxisome. They
initiate the conversion of fatty
acids to sugar for the growing
seedling to use as energy .and
carbon until it can produce its
own energy by photosynthesis
VACUOLES – LOADS OF CLOSET SPACE
My vacuoles serve the purpose of :
Containing small molecules ie CONTAIN FOOD
Maintaining internal hydrostatic pressure ie CONTAIN WATER
Containing waste products ie CONTAIN WASTE
PLUS
Isolating materials that might be harmful or a threat to the cell
Maintaining a constant internal pH
Exporting or importing substances from the cell
The majority of vacuoles are formed through the
fusion of vesicles. The vacuole has no basic shape
or size, but rather varies its structure according to
the needs of the cell. I use lipid vacuoles to store
excess energy efficiently in my fat cells.
Being an animal cell, most of my vacuoles
are related to the process of exocytosis
and endocytosis.
Hey boss, You know I’ve
got much bigger vacuole
than anything you saw
from that Mr Cell fella.
That’s right cause you
store lots of cellular
products. Stuff like
starch that you make
from the glucose
products of
photosynthesis
See that guy? He’s eatin’ a potato. That gives him a lot
of nutrition because of the starch stored in plant cellsspecifically the vacuoles. Plant cells typically store
their glucose as starch in those vacuoles. Starches in
corn wheat rice etc could be said to be responsible for
feeding most of the planet!
Plant cells have a central vacuole that is not found in animal vacuoles. They
mainly function as storage, and enlargement of this vacuole is a major
mechanism of plant growth. Other functions in plants include breakdown of
waste and hydrolysis of macromolecules. The tonoplast (plant cells only) is a
membrane enclosing the central vacuole.
CELL (PLASMA) MEMBRANE and the CYTOPLASM
My cell membrane forms an outer boundary for my structure. It is
one of the essential requirements of a cell that it has an enclosing
membrane. My plasma membrane is flexible and capable of
stretching or shrinking according to the amount of water inside my
cytoplasm. It is made up primarily of chemicals called phospholipids
and is responsible for also allowing certain things into or out of me.
More will be discussed in the MEMBRANE AND TRANSPORT powerpoint presentation .
The cytoplasm is a broad term that relates to cellular components other than
the nucleus. Since there is the ability to determine more precise structures
within the cytoplasm, it is divided into the organelles and structures discussed
previously and the cytosol. The cytosol comprises the liquid in the cell .
Don’t forget that I got a cell membrane
and cytosol too.
And I got a cytosol too.
I know I’m small and
their ain’t much but its
there for me to carry
out my metabolic
functions
CELL TO CELL CONNECTIONS --- IT’S ALL IN THE GRIP
Cell membranes can link cells together for
various purposes. The three types of
junctions are:
Tight Junctions – forming continuous seals
around cells to prevent passage of anything
through them.
All three are
typical in
epithelial
cells. Ex
intestinal
lining, skin,
Desmosomes – called anchoring
junctions- fasten cells together
Gap junction == called
communicating junctions provide
cytoplasmic channels from one cell
to another.
Review of Plant cell and Animal cell differences
Animal cells but not plant
cells
Plant cells but not animal
cells
lysosomes
chloroplasts
centrioles
Central vacuole and tonoplast
Flagella ( in some plant sperm) Cell wall
Plasmodesmata
Hey ! How come I ain’t
got those centrioles?
How come you ain’t got
centrioles boss?
Well, you don’t need them. Both
you and the animal cells have a
centrosome. The centrosome in
plant cells is all that is needed to
organizes your microtubules for
your mitosis division.
I divide by fission and I don’t have
chromosomes that I have to
organize! I just duplicate the short
DNA strand and divide.
CHLOROPLAST ; LIGHT makes GLUCOSE
Now it’s my turn. Now some of my cells contain chlorophyll and
are thus green because the active chemical in the chloroplast is
the green coloured chlorophyll. Chloroplasts contain all the
necessary enzymes and chemicals for me to complete
photosynthesis
Thylakoids (dark green)
Stroma (pale green)
Lamellae ( thin green lines)
Inner membrane
Think of the thylokoids as tiny green M&M’s. A
stack of these is known as a granum. More than
one stack are called grana. These are the sites that
actually contain the chlorophyll molecule in their
membranes.
Free ribosomes, the chloroplast’s own special
DNA and the chemicals involved in the Calvin
cycle are all located in the stroma
Outer membrane
There are actually three separate
compartments in the chloroplast.
! The intermembrane space between
outer and inner membranes
2.The stroma
3,the thylakoid space (inside a
thylakoid)
PLASTIDS – THE FORGOTTEN GROUPS
Most of my plastids are less well known because
the most popular is chloroplast. I have other
plastids like amyloplasts and chromoplasts
Amyloplasts are colourless
plastids that store starch in the
form of amylose
Chromoplasts are pigments
that give fruits and flowers
their orange and yellow
colours
CELL WALL – MULTIFUNCTIONAL PLANT UTILITY
Hey! You know, I also got
a cell wall but it’s made
of slightly different
chemicals
The plant cell wall
Protects the cell
Maintains shape
Prevents excessive water uptake
Hold the plant against the force of gravity
The polysaccharide cellulose is the prime ingredient and it forms
fibres called microfibrils that are embedded in a matrix of other
polysaccharides. This forms a strong material in much the same
way that steel reinforces concrete to make it much stronger.
Asjacent cell walls are glued together with pectins, a sticky substance
that attaches them together and forms a layer called the middle lamella.
Plant cell walls are typically perforated by holes call plasmodesmata.
Plasmodesmata allow the cytosol between cells to connect and provide
a chemical unity for the plant. Water and particular molecules can pass
through these channels as well as RNA and specific proteins.
Pectins are
used as a
thickening
agent in
jams.
PROKARYOTE OR EUKARYOTE?
It’s time to get to some serious points now kids. I’m a prokaryotic
cell. That means I don’t have a nuclear membrane. This can be
derived from the term pro = before and karyon= nucleus.
Eukaryotes on the other hand have a nucleus surrounded by a
nuclear membrane. Eu=true karyon= nucleus. Don’t be fooled
because my DNA is sometimes described as being found in a
region called the nucleoid– this is not a nucleus, just a region in
my cytoplasm.
I’m also a lot smaller than the eukaryotic cells. I’ve got smaller ribosomes,
(30s + 50 s) and my cell wall is made of chemicals different than those of
the eukaryotic plants. I am more restricted in my biochemical pathways
because I do not have the mitochondria to complete Krebs and ETC.
Goodbye from all of us. We sincerely hope that you
will remember us in your future!
The End
A tour of the Cell